1. Field of the Invention
The present invention relates to a position detection apparatus and a position detection program.
2. Description of the Related Art
A navigation device, used in a moving object, especially in an automobile, overlappingly displays an own-vehicle position on map data stored on a storage medium such as a hard disk drive, wherein the position is detected by using a radio navigation method such as a GPS (Global Positioning System) and a beacon; and an inertial navigation method such as a gyro and a vehicle speed pulse provided in an automobile main body and an in-vehicle terminal. Furthermore, the navigation device searches a route from the own-vehicle position detected on the map to a destination set by a driver and guides her/him to the destination.
However, an error is included in the own-vehicle position detected. The error is due to a sensor mounted on the automobile. For example, there are an error due to a multipath of a GPS, an error due to a wheel slip in using a vehicle speed pulse, an accumulation error of a gyro, and the like. Consequently, in order not to display a detected own-vehicle position away from a road where an automobile is travelling, there is a correction technology (map-match technology) to move the own-vehicle position to a position on the road.
Furthermore, an error is also included in road data of a map. Therein are included an error when the map data is made, and an error due to an approximation and expression of a road contour by a plurality of segments. Also with respect to road data including such errors, an own-vehicle position must be decided on a road along a route in order to guide a driver.
For that purpose is disclosed a vehicle-position detection apparatus that acquires road data around an own-vehicle position; calculates a similarity degree between a road contour and a vehicle travel orbit derived from a GPS, a vehicle speed sensor, and a distance sensor; and performs map-matching to a position on a road with a large similarity degree (for example, see Japanese Patent Laid-Open Publication No. JP H09-152343). The similarity degree is computed on the basis of a road azimuth, and a current position and travel azimuth of a vehicle.
Furthermore, a technology is disclosed that estimates a positioning error due to an inertial navigation method by: accumulating detection information of an autonomous sensor for detecting behavior information of an automobile; detecting an inertial positioning location of a moving object; applying an variance (hereinafter referred to as an “error variance”) with respect to an error of the inertial positioning location at a time t, and a sensor error variance and calculation error of the autonomous sensor to an update equation based on a moving-object model; and asymptotically calculating an error variance of a time t+1 (for example, see Japanese Patent Laid-Open Publication No. JP 2008-20365). According to the technology, it is determined whether position coordinates of an intersection node stored in a map data base of a navigation device is included in a reliability error ellipse generated from an error variance, and when it is included, an attention is drawn to a driver, and thereby a warning is given to her/him.
However, according to the technology described in the Japanese Patent Laid-Open Publication No. JP H09-152343, although information is calculated with respect to an own-vehicle position and an azimuth by using data obtained from a sensor, there is a limit to the accuracy of the map matching because a sensor error changing in time series is not considered.
Furthermore, according to the technology described in the Japanese Patent Laid-Open Publication No. JP 2008-20365, although an own-vehicle position and its error variance are sequentially updated by using the inertial navigation method, a radio navigation method such as a GPS is not used. Furthermore, noting only a relationship between the error variance and the intersection node of the map data base stored in the navigation device, the technology does not consider performing the map matching to road data where the map data base is used.
According to a conventional technology, when map-matching an own-vehicle position, which is calculated by using data including an error acquired from a sensor, to map data including an error, a foot of a perpendicular line is drawn to a road link in the map data from the calculated own-vehicle position, a Ucrid distance is calculated between the position and the foot, and the foot having a minimum distance is made the map-matched own-vehicle position. However, according to this technology, because the error of the calculated own-vehicle position is not considered, the map-matched own-vehicle position is largely displaced from an actual own-vehicle position in some cases.